I know I'm not the #1 most knowledgeable person about Transformers on these boards, but it has been pointed out to me that I do have quite a large repository of useless knowledge when it comes to the general history of Japanese pop culture, toys and robots. Thus, I've taken it upon myself to provide this board with a historical record of the evolution of giant Japanese transforming robots for those who might be interested in such a thing. So here goes...

Like many other cultures, the Japanese people have viewed the supernatural power of transformation as part of their heritage for centuries. The Japanese word bakemono (also obakemono, or obake) translates as "something that changes" and is used to descibe a type of mythological spirit, goblin or demon that can change its shape from one thing to another. A particularly interesting type of obake is the tsukumogami ("spirit of past 99"), which is an inanimate object of some kind that, upon reaching 100 years of age, is possessed by a spirit that can transform it into a goblin form. There are tsukumogami that transform from umbrellas, paper lanterns, shoes and even toys. So the concept of an inanimate object or tool transforming into a living creature is an old, old concept in Japan.

Statue of a Japanese obake kasa, or umbrella goblin.

Jumping forward to the mid-1880s, there were complicated clockwork toys and mannequins made in Japan that were designed to look like people and emulate simple tasks like serving tea or firing a bow and arrow. Thus, when the term "robot" was first coined in 1921 in Karel Capek's stage play R.U.R. (Rossum's Universal Robots), the idea of mechanically-created humanoids was already a familiar concept in Japan, as in many other countries where such creations had been around for many years.

First use of the word "robot" on the Czech playbill for R.U.R..

Possibly the first "robot in disguise" ever depicted in popular media was Maria the robot, seen in Fritz Lang's 1927 silent film masterpiece Metropolis. The metallic female robot is diguised to look like the human woman Maria, who is a proponent of the downtrodden workers who slave away under a futuristic city. Thus, when the human Maria is replaced by her evil robot double, the robot Maria becomes the first "pretender" in robot history.

^ The transformation of the robot double of Maria

As the robot grew in popularity, many different types were introduced in science-fiction novels and magazines of the 1930s. The image of the giant humanoid robot soon become commonplace on sci-fi pulp magazine covers, and carried over quickly into the new medium of superhero comic books and cartoons.

Cover art from the 1935 issue of the Amazing Stories sci-fi pulp magazine. Almost an Autobot, but not quite...

We now return to Japan. The year 1934 saw the very first Japanese comic strip "robot" that could change shape -- sort of. The simply-drawn, humorous comic strip was called Tanku Tankuro, the name of the main character. Tanku was a funny little robot samurai with a round metal body. From several large holes in his body, Tanku was able to pull various weapons and extend wings and propellers so he could fly. Regardless of whatever tools Tanku might extend from his spherical body, his smiling human head always remained on top.

Tanku Tankuro manga comics

The first appearance of what would evolve into the traditional giant Japanese robot was seen in a wartime political magazine cartoon from 1943 entitled "The Science Warrior Appears in New York". World War II was not going well for the Japanese at that point, and the idea of a giant robot warrior that could stomp New York City must have seemed like a wonderful dream.
"The Science Warrior Appears in New York" from a 1943 issue of Manga monthly comic magazine

Post-war Japan saw a boom in tin toy manufacturing, and of course robots became a popular theme. By the late 1940s and early 1950s, wind-up tin robot toys were commonplace in Japan.

The famous Japanese comic character Mighty Atom (better known as Astro Boy outside of Japan) made his first appearance in 1952, as drawn by the "god of manga", Osamu Tezuka. Astro Boy went on to become a popular cartoon in 1963, and it set the stage for the particular form of Japanese cartoon animation style known as anime. Although Astro Boy himself wasn't a giant robot or a transformer, a couple of the robot monsters he fought featured powers very much like those of the later "combiner" robots, such as a robot centipede that could separate into smaller robot parts and then recombine.

However, the first giant Japanese robot character was soon to appear...

The 1956 manga comic series Tetsujin 28-go ("Iron Man # 28", better known in the US as Gigantor) introduced the first giant Japanese robot character. Created by manga artist Mitsuteru Yokoyama, Tetsujin 28's pointy nose and resemblance to a medieval knight harks back to the "Science Warrior" WWII political cartoon discussed previously. Indeed, in Tetsujin 28's origin story it is revealed that he was developed during WWII as a weapon, but the war ended before T-28 was completed. T-28 is not a sentient robot, but is controlled from a distance by a remote control device. In 1963 Tetsujin 28 went on to become a popular anime TV series in Japan and soon after in the US as well (as "Gigantor").

Tetsujin 28 (AKA Gigantor), manga, & anime.

Another historically important Japanese robot character appeared in 1965, and this one was an actual transformer! ...Sort of.
The great Osamu Tezuka created the manga Ambassador Magma in 1965, and it was quickly made into a television series in 1966, becoming the first sci-fi hero vs monster TV show in Japan (beating the more famous Ultraman's premiere by one week). The TV series was later dubbed and shown in the US as Space Giants during the 1970s.
The giant living golden robot Magma (called "Goldar" in the US version), had the ability to transform into a golden rocket ship, making him technically the first transformer...but there's a catch. Goldar's transformation is not mechanically logical, and there is no clear shifting of parts to explain how his transformation works. In the TV series, there were close-ups of various robot body parts being covered by the hull of the rocket, but you never see where the rocket parts come from. Watch the video to see for yourself...

As we can see, Magma/Goldar's change to rocket is a bit more like magic or morphing than an actual mechanical transformation, so there couldn't be any toys of the character that could transform. Still, Magma technically holds the honor of the first giant robot-to-vehicle transforming character.
Magma (AKA Goldar), manga and live action version.

Another noteworthy early live-action robot appeared in the 1967 TV series Ultra Seven. The enemy alien robot "King Joe" was the first "combiner" robot made up of 4 different smaller machines. King Joe first battled the heroic Ultra Seven in the 2-part episode "The Ultra Garrison Goes West".
King Joe from Ultra Seven, the first live action combining robot.

1972 brought the first appearance of the manga Mazinger Z by manga artist Go Nagai, introducing the first Japanese "mecha" giant robot character. "Mecha" generally refers to a humanoid robot that is merely a vehicle for a human driver, and has no intelligence of its own. While there were several giant remote-controlled robot heroes on TV the 1960s like Tetsujin 28 or Giant Robo, these robots had no human pilots inside them. Thus, Mazinger Z introduced the concept and general visual design of the archetypical Japanese mecha robot. The Mazinger Z anime TV series also began in 1972, and set off a huge wave of giant robot cartoons that still continues in Japan to this day.

The first diecast metal toy figure of Mazinger Z was made by Popy toys in 1974, starting yet another proud ongoing Japanese tradition of the "chogokin" diecast robot series.
Mazinger Z art and original diecast "chogokin" toy.

In 1974, Go Nagai again made Japanese robot history by introducing the first anime robot vehicle combiner, Getter Robo. Getter Robo was formed from three non-transforming vehicles that could assemble in 3 different ways. The combination process seen in the cartoon was again a bit "fudged", so that it's a bit more like morphing in places. Thus, there were no toy versions of the Getter Robo vehicles that could actually combine like in the anime.

In 1975, the anime series Brave Raideen premiered on Japanese TV, and with it came the first "real" transformer in the form of the giant robot Raideen. Raideen was an ancient creation of a long-dead advanced civilization, and he was a living sentient robot. Despite being alive, he bonded with a young human man who was able to pilot Raideen. Raideen was able to transform into a giant birdlike jet called the Godbird, and this transformation was the first true "realistic" mechanical depiction of a robot transforming into a vehicle.

The diecast metal toy version of Raideen released by Popy in 1975 was the first transforming robot toy ever made. When the 5 inch tall diecast Popy Raideen was brought to the US as part of the "Shogun Warriors" toy line by Mattel in 1978, American kids got their hands on their first transformer (then called a "two-in-one warrior").

The Shogun Warriors series of toys also included robots from other popular Japanese anime series such as Grendizer, Great Mazinger and Getter Robo G. Five different super-robot anime series (Gaiking, Dangard Ace, Getter Robo G, UFO Robot Grendizer and Starzinger) were translated and brought to the US in 1980 as the Force Five TV series.

1979 Shogun Warriors ad

By the time The late 1970s rolled around, there were combiners, transformers and other super-robots all over Japanese TV. Some of the more famous late '70s anime combiners were Gaiking, Combattra V, and Voltes V. Late 1970s transforming anime robots included Daimos and Daitarn 3. The first live-action TV fully transforming robot was Daitetsujin 17 (1977). The 1978 live action Japanese Spider-Man TV series featured a high-tech Spidey who piloted a transforming robot named Leopardon that could change into a spaceship. In 1979 the already-popular "Super Sentai" series of TV shows (that would eventually become Power Rangers in the US) would follow suit by introducing a giant robot for its heroes to pilot in the series Battle Fever J.

Diecast transforming armored truck robot Daimos, made by Popy, 1978

1979 Also saw the premiere of the historic anime Mobile Suit Gundam. Gundam introduced the genre of the "real robot" series, as opposed to the "super-robot" series that had existed so far. The "real robot" aspects of Gundam centered on the fact that the main storyline was about the human characters and their lives, with the mass-produced giant robots existing in the background as war machines. The robots in the original Gundam series were not transformers, but this would change in later Gundam series during the mid-1980s.
1979 Mobile Suit Gundam RX-78 Gundam robot

As the 1980s began, there was at first still plenty of carryover from the colorful "super-robot" genre of the 1970s. Combiner robots were still plentiful, with some noteworthy examples being GodSigma (1980), the first combiner formed from smaller humanoid robots instead of vehicles, and of course Golion (1981) and Dairugger XV (1982), which would both end up as the dubbed US series Voltron, Defender of the Universe.
Godsigma, Golion and Dairugger XV

However, there was also an ongoing attempt to incorporate the dramatic "real-robot" aesthetics established in Moblie Suit Gundam, as seen in various anime shows featuring giant robots such as Ideon, Space Runway (1980), Dougram (1981) and Xabungle (1982).
l-r: Ideon, Xabungle, Dougram

These attempts were met with modest success until the 1982 TV premiere of Super Dimension Fortress Macross. This anime succeeded in combining the human drama, romantic intrigue and realistic mecha that older fans were hungry for. Macross was an immediate success, and its transforming Valkyrie aircraft designs set a new standard for "perfect transforming" robot designs that looked functional and cool in both vehicle and robot modes.

Macross, along with the similarly-themed anime Mospeada (1983) and Southern Cross (1984), would all be dubbed and combined into the Robotech TV series, which premiered in the US in 1985. Macross toys in particular were hugely popular in Japan, and jumpstarted the transforming robot toy craze from 1982 onward.
Macross transforming VF-1S Valkyrie toy by Takatoku. This toy would later become the Transformer Jetfire.

Very nice write-up on the history of transforming robots, Lizard. Ever since I was young, I had obsessed with Japanese robot toys and animations, with Macross, Voltron, Mazinger-Z as some of my favorites. I think you left out a combiner robot which had 15 vehicles combing to form one gigantic robot (I forgot the name). What's striking about this combiner is that those 15 can form into 3 teams of 5, one for air, another for land, and last one for sea. Each team is also a mini combiner team, because the 5 vehicles can combine to become an unique vehicle, although none of the vehicles can become a robot, only when all 15 combine at once. I own the toy when I was young and I had fond memories of it.

__________________"I know I'm asking a lot, but the price of freedom is high, it always has been, and it's a price I'm willing to pay. And if I'm the only one, then so be it. But I'm willing to bet I'm not." - Captain America

I think you left out a combiner robot which had 15 vehicles combing to form one gigantic robot (I forgot the name). What's striking about this combiner is that those 15 can form into 3 teams of 5, one for air, another for land, and last one for sea. Each team is also a mini combiner team, because the 5 vehicles can combine to become an unique vehicle, although none of the vehicles can become a robot, only when all 15 combine at once. I own the toy when I was young and I had fond memories of it.

You're thinking of Dairugger XV, also known as Vehicle Voltron in the US. I do mention him briefly at the beginning of chapter V above, with a link to the YouTube video of the opening titles.

However, you do raise a point -- I'm not attempting to cover EVERY Japanese robot, whether combiner or transformer. There's just too many of them. I'm just trying to point out a few of the more noteworthy ones. Dairugger is kind of noteworthy, since he set the record for most vehicles making up one robot.

Personally, I wish that Michael Bay would pay some homage to Japanese or a nod for them for creating Transformers in the first place. But with GM cars and focus on U.S. military, you don't get a sense where Transformers come from in the first place.

__________________"I know I'm asking a lot, but the price of freedom is high, it always has been, and it's a price I'm willing to pay. And if I'm the only one, then so be it. But I'm willing to bet I'm not." - Captain America

Personally, I wish that Michael Bay would pay some homage to Japanese or a nod for them for creating Transformers in the first place. But with GM cars and focus on U.S. military, you don't get a sense where Transformers come from in the first place.

They'd have to go through their US branches though. And if Alternators Windcharger is any indication they might insist they neuter them.

__________________
I for one welcome our new red flamed, fish-lipped savior. May he always defend us from the scrap metal Devil.

1976 - Microman figures and vehicles brought to the US and sold by Mego as "Micronauts"

1980-81 - Takara introduces the "New Microman" toy line featuring the 3.75 inch tall miniature cyborgs with new special battle machines and playsets.
A spin-off toy line from this is also introduced by Takara, called Diaclone (AKA "Diakron") - a series of vehicles and combiner robots that are driven by human-sized cyborg pilots. The scale of these toys is 1/64, so the pilot figures are only one inch tall. The original 1980-81 Diaclone robots (mostly combiners) were designed by Shoji Kawamori and Kazutaka Miyatake, who would later go on to design the mecha for Macross.
1980 Diaclone catalog

1982 - The first two transforming "Car Robots" are introduced as part of the Diaclone line. These will later go on to be released in the US as the Autobots "Sunstreaker" (after a color change to yellow) and "Ironhide", so these are technically the first of the Transformers.
1982 Diaclone catalog

Also in 1982 - Popy releases the first toys in its transforming "Machine Robo" series, that will later be released as Gobots in the US by Tonka in '84 .

1983 - Another spinoff from the New Microman toy series debuts from Takara - "MicroChange", a series of minature robots and vehicles disguised as life-size tools and houshold items. This first wave of MicroChange toys includes several robots that will go on to be Transformers, including the Walther P-38 "Gun Robo" (Megatron) and "Cassette Man" (Soundwave). Also included in this first wave of MicroChange are the "Mini Car Robo" robots, intended to be disguised as toy "penny racer" cars. These will later become the Transformers mini Autobots "Cliffjumper", "Bumblebee", "Gears", "Brawn", "Windcharger", "Huffer", and the so-called "Bumblejumper".
Microman/MicroChange 1983 catalog page

Finally and perhaps most importantly, 1983 was the year that Hasbro representitives visited the Tokyo Toy Fair, saw the potential in the Diaclone and MicroChange toy lines, and made the historic deal with Takara to market these toys in the US under a new name and storyline.

1982 - The first two transforming "Car Robots" are introduced as part of the Diaclone line. These will later go on to be released in the US as the Autobots "Sideswipe" and "Ironhide", so these are technically the first of the Transformers.
1982 Diaclone catalog

Sunstreaker you mean. Diaclone Sunstreaker never came in yellow. Sideswipe did. And black and red, and a police version.

__________________
I for one welcome our new red flamed, fish-lipped savior. May he always defend us from the scrap metal Devil.